7. Simulation of a reactor core condition

A simple example was prepared to show the capability of the AZKIND code running with NK-TH coupling, and the thermal-hydraulic effect on power distribution is compared to the power distribution resulted from the NK model running standalone.

This example was prepared for a two energy group, that is, fast neutrons and thermal neutrons. In LWR, the nuclear fissions of the fuel atoms are mainly coming from the thermal neutrons present in the reactor core. The effect observed in Figure 7 is that the TH feedback induces an increase in the thermal neutrons population and so increasing power. As the coolant/moderator enters the reactor core through the bottom part of the reactor and the core

Figure 7. Axial power peaking profile location.

step function in the neutrons removal capability during 3 s is implemented in the perturbed assembly, after that the perturbation finishes and the transient lasts for two more seconds, giving a reactor power reduction. The time step used in this simulation was 0.1 s. Figure 6 shows the power behavior over time, departing from a normalized value of 1.0 and reducing the power reactor to almost 80% of its original value. This reactor power transient was simulated with the AZKIND code, running on the three different GPUs listed in Tables 2 and 3. The right side of Figure 6 shows the time spent by AZKIND in a logarithmic scale, running

in a sequential mode (Serial bar) and the times spent by each GPU card.

Figure 6. Simulation of a reactor power transient—serial and parallel processing.

Figure 5. A map of fuel assemblies in an LWR [1].

20 New Trends in Nuclear Science

is beginning the production cycle, the core design allows more power generation in the first third of the core active fuel. Also, as it was expected, in the map of fuel assemblies of the reactor core, the location of the fuel assembly with the highest generation of thermal power remained unchanged with the insertion of TH feedback.

5. CNFR: See [21]. This reference summarizes three methods, implemented for multi-core CPU and GPU, to evaluate fuel burn-up in a pressurized light water nuclear reactor (PWR) using the solutions of a large system of coupled ordinary differential equations. The reactor physics simulation of a PWR with burn-up calculations spends long execution times, so that performance improvement using GPU can imply in a better core design and thus extended fuel life cycle. The results with parallel computing exhibit speed

improvement exceeding 200 times over the sequential solver, within 1% accuracy.

The state of the art in the topic of nuclear reactor simulations shows significant advances in the development of computer codes. A wide range of applications focusing, besides on improving nuclear safety, on more efficient analyses to improve fuel cycles/depletion have been found in a recent study. A considerable "saving time" factor in obtaining nuclear reactor analyses has

One important part of a nuclear reactor simulator is the benchmarking process to demonstrate reliability and repeatability in the simulation of real cases, for which data from reactor operation or comprehensive data from experiments are well documented. In this sense, extensive documentation is necessary for theoretical basis, numerical techniques and tools, and valida-

, Armando Miguel Gómez-Torres<sup>1</sup>

1 Instituto Nacional de Investigaciones Nucleares, Ocoyoacac, Edo. de México, México

2 Instituto Politécnico Nacional, Escuela Superior de Física y Matemáticas, Col. San Pedro

[1] Rodríguez-Hernández A, Gomez-Torres A, Del Valle-Gallegos E. HPC implementation in the time-dependent neutron diffusion code AZKIND. Annals of Nuclear Energy. 2017;99:

[2] Oka Y, editor. Nuclear Reactor Design. (Series) An Advanced Course in Nuclear Engi-

\* and

Nuclear Reactor Simulation

23

http://dx.doi.org/10.5772/intechopen.79723

9. Conclusions and remarks

tion of both codes and simulation models.

\*Address all correspondence to: armando.gomez@inin.gob.mx

been observed.

Author details

References

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Zacatenco, Cd. de México, México

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Edmundo del Valle-Gallegos<sup>2</sup>
